Both options are valid because they have happened before and can influence the mentioned drop in the population. Toxins in the food chain, just like the increase of water temperature, are easily proven and found and are mostly human made.
1.herbivory
2.predation
i dont know the other two sorry
p = m / V (Density = Mass / Volume)
p = m / (w * l * h) (Density = Mass / [Width * length * height]) (V = w * l * h)
p = 120 / (5 * 4 * 3) (Mass = 120g [Given] w=5 l=4 h=3 [Given])
p = 120 / 60
p = 2 g/cm^3
Answer is B (2)
